NFkB is a critical transcription factor regulating expression of pro-inflammatory and anti- apoptotic genes. Previous studies from our laboratory demonstrated that as opposed to other cell types, resting human neutrophils contain predominant amount of NFkB inhibitor, IkBa, in the nucleus, and this increased nuclear accumulation of IkBa results in the inhibition of NFkB activity and increased rate of neutrophil apoptosis. Our recent data have shown that proteasome inhibition induces translocation of IkBa to the nucleus in leukemia HL-60 and U- 937 cells, and in cancer HeLa cells; however, the mechanisms are currently unknown. The central hypothesis of this proposal is that induction of nuclear accumulation of IkBa inhibits NFkB activity and expression of NFkB-regulated anti-apoptotic and pro-inflammatory genes, and could thus provide a basis for novel anti-cancer and anti-inflammatory therapies aimed at the inhibition of NFkB activity by the nuclear IkBa. The specific aims focus on analyzing the mechanisms by which the nuclear IkBa inhibits NFkB activity and expression of NFkB-regulated genes in leukemia HL-60 and U-937 cells. In Aim 1, we will test the hypothesis that the proteasome inhibition-induced nuclear translocation of IkBa results in the inhibition of NFkB activity and decreased expression of NFkB-regulated anti-apoptotic genes, by using transfection of HL-60 and U-937 cells with inhibitory IkBa RNA. In Aim 2, we will use chromatin immunoprecipitation to test the hypothesis that the nuclear IkBa inhibits NFkB activity by associating with the promoters of NFkB-regulated genes. In Aim 3, we will investigate the mechanisms that regulate the proteasome inhibition-induced nuclear translocation of IkBa. Identification of the key molecular events that control NFkB activity by the nuclear IkBa will broaden our understanding of the mechanisms regulating NFkB activity, and might provide a new class of drug targets to regulate the NFkB driven pro-inflammatory and anti-apoptotic gene expression. The focus of this proposal is to identify the mechanisms by which the nuclear translocation of IkBa regulates activity of the transcription factor NFkB. Since NFkB activity is increased in many human diseases including inflammatory disorders, cancer, and leukemia, identification of the mechanisms by which the nuclear IkBa inhibits NFkB activity will contribute to the development of novel anti-cancer and anti-inflammatory therapies. [unreadable] [unreadable] [unreadable]